4g towers transmit downward to users in the city below them. They do not transmit upward.

That is why if you leave you phone turned on during a commercial flight, it will stop working after take off anyway. The towers don't send signal upward. You might still collect some residual signal for a little bit if you are near a tower and directly above it for a thousand feet or so, but not at 14,000 ft.

This couldn't be done with a 3g/4g/5g/LTE modem.